Some tiles are ~solvable without building anything.

Sometimes this is dead-simple (the balls just drop from the top on through).

Sometimes, they'll solve if you're patient enough (the balls pile up, shift around, and sooner or later enough of them exit within the time window necessary to trigger the submit UI).

Edit: to finish connecting the dots just in case--I waited quite a while for one, probably at least 10 minutes--to do this. When the clearance rate for a machine is poor, it will usually drop back under the submit threshold very quickly. In these cases, you have to watch very carefully to be prepared to submit in the brief window that the submit UI is enabled. The OP suggests that during moderation they generally waited 30 seconds for a submitted machine to do the thing before they moved on.

We also set up the minimum requirement for the submit button to be unlocked to not be too strict, to avoid frustrating people, but held a bit of a higher standard for the things we selected to be part of the public machine. So designs that only just barely work well enough to occasionally unlock the submit button are probably too unreliable to get selected for inclusion (but we made occasional rare exceptions if the submission was particularly interesting / inspired for other reasons).